Here is some information about the Septuagint that explains how the Jews and early Christians came to accept the writings that make up what is called the Christian Bible: What is the Septuagint?
>>Who get s to decide? Well, anyone can add any books they want to the Bible, but that doesn't make them Scripture in the classic sense.<<
But who gets to decide what is Scripture in the classic sense? Christianity had a consensus on the Bible for 1500 years until the Protestants remove the Deuterocanonical / Apocryphal books.
I know you think you are defending the Roman Catholic recognition of the Deuterocanonical/Apocryphal books as equal to the Divinely-inspired Old and New Testament books accepted by ALL Christian traditions, but you are misinformed about many points here. Here is an additional link that will help:
What are the Apocrypha/Deuterocanonical Books?
This will also be helpful to explain why the Apocryphal books were not counted as in the canon of the Bible:
Yes, I meant the Deuterocanonical books.